So i would like to use the mother-in-law unit [part of the house] for my stay and rent 1700 square feet to a middle age or senior couple.  

If we're close we'll usually write an LOI quickly to lock the property up but if we're way far off I will generally ask the seller/agent (we try to negotiate direct to seller as much as possible and stay away from listed properties), if it even makes sense to write it up. 

Welcome to another fellow NY'er feel free to stay in touch and keep the network alive and good luck on your investments 

I think the carpet is literally 100 yrs old.  

They are then faced with gambling that rates will stay low until they can refinance or sell the asset.So how do forward commitments work?

If the bedroom carpets are ten years old, and they have wear from where they were walked on, I wouldn't charge them.

It's in relatively good shape, hardly any issues, and the current tenant is very cooperative and responsible, he intends on staying for at least another 2 years.I'm seeing this as an opportunity for my first buy-and-hold property.

I believe the primary residence can be rented for about $2500 if the rents stay relatively stable.  

I’m trying to stay a bit conservative with my future predictions for this particular area.

Tenants tend to stay in SFH's longer than apartment rentals, so I would assume 3-4 years, and turn over could be as simple as a wipe down and carpet cleaning if the PM is doing their job and screening tenants appropriately (although even great screening doesn't always guarantee great, clean tenants).